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I have a new Alpine install and I'm having trouble with pump cavitation when the supply temp is over ~160 deg. The system seems to be plumbed correctly with a 1" primary, a 1" DHW loop on priority, and two 3/4" baseboard zones (all with Grundfos 3-speed pumps). The pumps on are on the supply side just after the expansion tank. The expansion tank seems to be correctly sized and is working properly (no measurable pressure fluctuation with temp). System pressure is reading ~15 psi.
This is a retro into a system that needs ~170 water to match heat loss on cold days.
The DHW can run at 170 and both the boiler pump and the DHW pump are silent, but during a prolonged heat call both of the zone pumps will get noisy when the set point rises past 160 deg.
Other than raising system pressure, I don't have any ideas. I would re-plumb if I saw an obvious problem but I don't. Any ideas?